1. Field of the Invention
The present invention relates to a connection material for connecting a flexible circuit board to a bare IC chip, this connection material causing substantially no shoulder touch effect.
2. Description of the Related Art
Tape carrier packages (TCP) in which a driver IC was mounted onto a tape-like substrate have been used for the manufacture of liquid-crystal display element modules, but in order to meet the requirements imposed by the transition to a narrower wiring pitch and to facilitate processing operations in assembling with a liquid-crystal display element module, a CHIP ON FILM (COF) method came to use, this method involving face-down direct mounting of a bare IC chip onto a conductor pattern of a film-like flexible circuit board which is even thinner than the tape-like substrate for TCP.
In such COF connection, as shown in FIG. 3, a bump 5 of a bare IC chip 4 is positioned against a conductor pattern 2 of a film-like flexible circuit board 3 containing an insulating film 1 and the conductor pattern 2 formed thereon, an anisotropically electroconductive film 6 in which conductive particles for anisotropically electroconductive connection are dispersed in a thermosetting adhesive film is sandwiched therebetween and bonded under pressure and heating.
If the bare IC chip 4 is connected by using the anisotropically electroconductive film 6, the insulating film 1 of the film-like flexible circuit board 3 undergoes thermal shrinkage after the connection and, as shown in FIG. 4, the flexible circuit board 3 located outside the bare IC chip 4 warps toward the bare IC chip 4. Since the bump height of bare IC chip 4 has been about 20 xcexcm the bare IC chip 4 has not been brought in connection with the conductor pattern 2 of the flexible circuit board 3.
However, as the wiring rule of IC chips was further refined, the number of terminals was increased, the terminal pitch was made smaller, the bump diameter of bare IC chips was reduced, and the bump height was also greatly decreased to about half of that in the conventional structures. As a result, as shown in FIG. 5, the bare IC chip 4 was sometimes brought in connection with the conductor pattern 2 of the flexible circuit board 3. Since a passivation film 7 is formed on the lower surface of bare IC chip 4, no short circuit occurs despite the connection, but the problem is that because the passivation film 7 cannot be formed on the scribe line portion 8 provided to cut out the bare IC chip 4 from the wafer, short circuit sometime occurred, in particular, in the shoulder edge portion 9 of bare IC chip (shoulder touch effect) and the insulation resistance between the adjacent conductor patterns 2 decreased significantly.
An object of the present invention is to provide a connection material which causes no shoulder touch effect when a flexible circuit board is connected to a bare IC chip.
The inventors have found that the object of the present invention can be attained by admixing a flaky or fibrous insulating filler to a connection material for connecting a film-like flexible circuit board and a bare IC chip. This finding led to the completion of the present invention.
Thus, the present invention provides a connection material for connecting a flexible board to a bare IC chip, comprising an insulating adhesive and a flaky or fibrous insulating filler dispersed therein.